CDMA Transmission Model
An Overview in Matlab
Engr. Abdul Basit
Saad Najaf Khan09-ECT-38
15th June, 2012
UNIVERSITY OF ENGINEERING AND TECHNOLOGY TAXILA
SUB CAMPUS CHAKWAL
CDMA is modulation technique to transmit data over a whole frequency spectrum. It was developed by Qualcomm as a better technology to TDMA based 2nd Generation GSM. In many aspects, such as power, security, number of users, and efficiency, it achieved success in displacing TDMA as the preferred technology. According to recent statistics by CDG, CDMA is used in 1/3 of wireless technologies, with 60% of the subscribers in Asia Pacific Region. CDMA – An overview:
The following model figure shows the major parts to a CDMA system. There are four parts to simplex transmission. 1. Transmitter: The data is first encoded using a unique code called PN sequence (discussed in detail on next page) and then RF modulated. The final signal is the transmitted through a physical channel. 2. Receiver: The incoming signal is first RF demodulated then decoded to get the intended signal. The decoding is again done using a unique code, same as transmitter.
Figure.1: Overview of CDMA Simplex Transmission System
PN Sequence a.k.a Spreading Sequences:
CDMA is a spread spectrum based modulation technique. The PN sequence is applied to the input signal to achieve the desired spreading effect. Types:
There are different types of spreading sequences. They are selected on the basis of autocorrelation & cross-correlation properties and usage type. The four major of them are listed below: 1. Maximum length Pseudo Noise (PN) sequence a.k.a M-sequence: Maximum Length is a reference to binary sequence generators proficient in outputting the...